This invention relates to bladeless shearing of linear stock such as stainless steel tubing and bar stock and, more particularly, to a device which achieves the shearing of stock by causing elliptical, lateral translation of a section of the stock relative to an axially adjacent section.
In U.S. Pat. No. 4,635,514 xe2x80x9cElliptical Shearing Apparatusxe2x80x9d, issued Jan. 13, 1987 to Alexander Borzym, there is disclosed a bladeless device for shearing linear stock, such as bar stock and tubing, by causing a section of the stock to translate laterally through an elliptical path relative to the axially adjacent stock. As is more fully disclosed in the aforesaid patent, this is achieved through the use of a large, steel body referred to as a xe2x80x9cdie holderxe2x80x9d having a central, die-like aperture formed therein which is adapted to receive and precisely surround the linear stock. One side of the die holder is pinned to permit pivotal and limited lateral motion. The other side is connected to a drive mechanism consisting of a large electric motor driving a flywheel at constant speed and a clutch and brake mechanism for selectively and momentarily imparting orbital motion to the die holder. Orbital motion of the die holder around the mechanical drive center produces a unidirectional, elliptical translation of the stock receiving die which lies between the drive center and the pinned end of the die holder. The amplitude of the elliptical motion is a function of the amplitude of the orbital drive motion and the geometric location of the die within the die holder body.
By placing a fixed die also having a stock-receiving aperture immediately axially adjacent to the moveable die, a scissors-like shearing action is produced on a length of stock which is inserted through the two aligned dies; the shear line is defined by the mating plane of the two dies.
There are numerous advantages to a shear of this type relative to cutoffs using blades or other cutting implements. The principal advantages are the elimination of the cutting implement as a perishable component and the conservation of material in the work piece; i.e., saw blades and guillotine blades remove a section of material approximately equal to the thickness of the blade each time it passes through the stock. The resulting loss of material from the stock is significant, particularly where short lengths and high cutting rates are employed.
Another advantage is the quality of the xe2x80x9ccutxe2x80x9d which can be achieved in the use of the bladeless shear in connection with stock of very hard material such as stainless steel. Blade type cutoffs are known to cause distortion; e.g., burrs and/or dents in the cut tube ends, and very high blade wear when used with hard materials such as stainless steel. The bladeless shear cutoff actually excels when used with materials of this type.
It has been found that the highest quality result of a bladeless shearing operation is achieved when the amplitude of the die stroke is minimized in relation to the wall thickness of the stock. For example, the optimum shearing quality for tubular stock of low ductility occurs when the maximum relative die translation is approximately equal to the wall thickness of the tubular stock. Since the machine of U.S. Pat. No. 4,635,514 had a fixed stroke, i.e., a fixed dimension of the elliptical path followed by the orbital ram, the optimum performance of the machine was confined to a narrow range of stock. We have, therefore, provided a bladeless shear device in which the stroke is adjustable.
Another advantage of the adjustable stroke in an orbital or elliptical shear is the distribution of the shearing action over a large angular movement of the tooling. This greatly reduces the tendency of prior art shear devices using an L-shaped path and non-adjustable stroke length to xe2x80x9cdrawxe2x80x9d the stock in the shear area.
Through the invention disclosed herein, the drive system of the aforesaid ""514 patent has been improved by, in particular, eliminating the clutch and brake mechanism in favor of a direct xe2x80x9clinearxe2x80x9d drive. Specifically, a reversible linear drive is provided through which the orbital wheel is reversibly driven through successive single revolutions in alternately opposite directions. Relative to prior art systems, this reversible drive promotes longer tool life through more efficient tool edge usage. In one form, the drive comprises hydraulic cylinders driving opposed linear racks which oppositely engage a pinion on the drive shaft of the orbital wheel in the moveable ram. The cylinders are powered by oil from a pump and oil pressure can be managed to provide numerous advantageous results hereinafter described.
In another form, the drive comprises an electrical drive using a reluctance motor and a gear reduction system engaged to the pinion.
It has further been found desirable to provide hydraulic clamping of the work piece and mandrel and a readily adjustable in-feed table which is useful in feeding tubular stock into the shear mechanism during a repetitive shearing operation. This table works in conjunction with novel forms disposed on the mandrel rod to prevent the rod from sagging. These and other advantages of the inventions will be best understood by reading the following specification which describes illustrative embodiments of the inventions in detail.